Wetland food resources for spring‐migrating ducks in the Upper Mississippi River and Great Lakes Region

Abstract

Wetlands in the Upper Mississippi River and Great Lakes Region (UMRGLR) must annually sustain populations of migrating waterfowl from the mid‐continent of North America. We used multi‐stage sampling to estimate plant and invertebrate food biomasses (kg/ha) for ducks in 3 wetland habitat types at 6 stop‐over locations in the UMRGLR during 2006 and 2007. Total biomass was greatest in palustrine emergent (PEM; ${\bar {x}}$ = 208 kg/ha, SE = 23, median = 120), followed by palustrine forested (PF; ${\bar {x}}$ = 87 kg/ha, SE = 7; median = 43), and lacustrine–riverine (LR; ${\bar {x}}$ = 52 kg/ha, SE = 7; median = 27) wetlands. Ducks that foraged in forested and LR wetlands encountered the least food abundance during spring in the UMRGLR. Our estimates of food abundance were the lowest reported among other landscape scale surveys from mid‐continent North America. About 1 in every 5 PEM wetlands and over half of our PF and LR wetlands that we sampled contained <50 kg/ha of food, suggesting many had little or no forage value to ducks during spring. Biomass of plant foods generally exceeded invertebrate biomass in all habitat types, although invertebrate biomass estimates exceeded plant biomass in 8 of 29 sites when considered by wetland type and year. Total food biomass estimates varied widely (${\bar {x}}$ = 6–425 kg/ha) between years and among habitats; thus, using global arithmetic means to estimate food abundance for conservation planning obscures fine scale temporal and spatial variation that may be necessary for management on local and sub‐regional levels. Distributions of food biomass estimates were right‐skewed, causing us to question whether arithmetic means realistically represent levels of food abundance that all ducks encounter during spring migration. Alternative measures of central tendency (e.g., median) may be more biologically realistic, particularly if spring‐migrating ducks are not distributed in an ideal‐free manner with respect to food abundance. Future research should determine how ducks distribute themselves in relation to variation in food abundance in space and time during spring migration to strengthen the biological approach to conservation planning in non‐breeding Joint Venture areas of the North American Waterfowl Management Plan. © 2011 The Wildlife Society.

Mallard survival, movements, and habitat use during autumn in Illinois

“…Additionally, existing statutory refuges should be managed to maximize forage, thereby increasing mallard survival during autumn. When managed effectively, these refuges could provide resources needed during subsequent spring migrations, when food resources may be limited (Straub et al , Hagy et al ). Finally, the integration of people‐ and waterfowl population‐based objectives for habitat conservation under the North American Waterfowl Management Plan requires information describing waterfowl vulnerability to harvest and its impacts on hunter satisfaction.…”

Notice: The authors have discovered an error in raw data analyzed in this paper. This article has been retracted. The corrected article is published online early as Ringelman KM, Williams CK, Castelli PM, Sieges ML, Longenecker RA, Nichols TC, Earsom AD. 2018. Estimating waterfowl carrying capacity at local scales: A case study from Edwin B. Forsythe National Wildlife Refuge, New Jersey. Journal of Fish and Wildlife Management 9(1):xx-xx; e1944-687X. doi:10.3996/082017-JFWM-066.

“…This variation in supply may be real; that is, no amount of core sampling will reduce estimates of variance in a habitat that is inherently variable. In cases such as ours where managers believe the estimated variation is not due to insufficient sampling (Ringelman et al 2015a), making decisions based on the mean or median value may be the best course of action (Straub et al 2012). Further research on the underlying drivers of this variation in habitat quality-and mechanisms to manipulate them-may prove to be fruitful investments.…”

Worth the reward? An experimental assessment of risk‐taking behavior along a life history gradient

“…Our goal with this treatment density was to reduce confounding between food density and other variables which may influence duck behavior such as vegetation density and overwhelm the background food level so that the treatment was the primary cause of variation in food density between plots. The density we selected represents a density that is much greater than any published estimate of natural food biomass (Kross et al 2008, Hagy and Kaminski 2012, Straub et al 2012, Olmstead et al 2013, VonBank et al 2016). The adjacent control plot did not receive any corn.…”